Electromagnetic shield structure

ABSTRACT

An electromagnetic shielding structure including at least a first transparent substrate, a conducting element, optionally a transparent backing sheet and a transparent tie sheet and a transparent additional sheet or covering sheet, and an electrical connector configured to be connected to the conducting element to ground the conducting element. At least one of the backing sheet, the tie sheet or the additional sheet or covering sheet, when present, is, at least on one of its sides, placed set back toward the interior of the structure relative to the associated free edge of the transparent substrate so as to leave a portion exposed on at least one of the faces of the conducting element, the connector being placed against and/or connected to this exposed portion.

FIELD OF THE INVENTION

The subject of the invention is an electromagnetic shielding structure,the invention relating more particularly to the electrical grounding ofthis structure.

DISCUSSION OF THE BACKGROUND

An electromagnetic shielding structure is, for example, used in adisplay, such as a plasma display.

A plasma display has a plasma gas mixture (Ne, Xe, Ar) trapped betweentwo glass plates, and phosphors placed on the internal face of the rearplate of the display. Ultraviolet light radiation emitted by the plasmagas mixture during the plasma discharge between the two glass platesinteracts with the phosphors on the internal face of the rear plate inorder to produce the visible light radiation (red, green or blue). A gasparticle deexcitation mechanism competes with the UV emission, whichgenerates infrared radiation between 800 and 1250 nm, the propagation ofwhich radiation, mainly through the front face of the display, may bethe source of very troublesome interference, especially as regardsequipment located nearby and controlled by infrared, for example bymeans of remote controls.

Moreover, like all electronic apparatus, plasma displays possessaddressing systems (drivers) that may generate parasitic radiation whichmust not interfere with other devices, such as microcomputers, mobiletelephones, etc.

To eliminate, or at the very least attenuate, the propagation of suchradiation, one solution consists in placing against the front face ofthe display a structure that is both transparent and metallized in orderto provide electromagnetic shielding.

A known example of a shielding structure, as illustrated in FIG. 1,comprises two glass substrates 10 and 11 between which two PVBthermoplastic sheets 12 and 13 and a PET sheet 14 are sandwiched, acopper mesh 15, constituting the conducting element forelectromagnetically shielding the structure, being deposited byphotolithography on the PET sheet 14, the latter being sandwichedbetween the two PVB sheets 12 and 13. The electrical connection of thecopper mesh to ground is performed by means of flat conductors, such asbusbars 16, soldered on one side to the copper mesh 15 and connected, onthe other side, to a grounded metal frame 17. This metal frameconstitutes the frame of the display and serves as support for theshielding structure associated with the display.

To keep the flat conductors 16 in position, for the purpose of solderingthem to one of the faces of the copper mesh 15, the conductors form areturn over the edge of the PET sheet 14 and the soldering takes placewhile the PET sheet and the PVB sheets are being joined together byheating the thermoplastics.

However, improper handling of the PVB sheets and/or incorrect joining ofthe PVB sheets to the PET sheet with the conductors may result indefects in the structure, such as blisters between the plastic sheets.Such defects are visible to the naked eye and such a product thereforecannot be used in displays.

In addition, the operation of folding the flat conductors over the edgeof the PET sheet and of bonding them thereto, in a suitable manner andwithout any defects, in order to form the returns, is not a rapid stepin an industrial manufacturing process. Furthermore, if thisfolding-over is poorly implemented, it may result in a breakage at thecorner of the returns.

Consequently, the joint dependence of the electrical connection means,consisting of the flat conductors, on the conducting shielding elementand on the PET backing sheet of the conducting shielding element doesnot allow the shielding structure to be easily manufactured.

SUMMARY OF THE INVENTION

The object of the invention is therefore to alleviate these drawbacks byproposing an electromagnetic shielding structure that allows simplerconnection of the conducting element of the structure to the electricalground, for example the display with which said structure is associated.

According to the invention, the electromagnetic shielding structurecomprising at least a first transparent substrate, a conducting elementdeposited on a transparent plastic backing sheet or else deposited onthe first substrate, and a transparent plastic tie sheet that ties theconducting element to the substrate by the backing sheet being joined tothe tie sheet, or else that covers the conducting element when thelatter is deposited directly on the substrate, it being possible for atransparent additional sheet or covering sheet to be optionally joinedto the backing sheet against the opposite face to the face joined to thetie sheet or else possibly being optionally joined to the tie sheet whenthe conducting element is deposited directly on the substrate,electrical connection means being intended to be connected to theconducting element in order to ground the latter, is characterized inthat one at least of the backing sheet, the tie sheet or the additionalsheet or covering sheet, when it is present, is, at least on one of itssides, placed set back toward the interior of the structure relative tothe associated free edge of the transparent substrate so as to leave aportion exposed on at least one of the faces of the conducting element,the connection means being placed against and/or connected to thisexposed portion.

What are called the faces of the conducting element are the surfacesthat extend over the largest dimensions.

In a first embodiment, the structure, with the conducting elementdeposited on the backing sheet, is characterized in that the element issandwiched between the tie sheet and the backing sheet, and at least thetie sheet is, on at least on of its sides, placed so as to be set backrelative to the associated free edge of he transparent substrate so asto leave space for a free part of the transparent substrate and for anexposed portion of the conducting element, this free part facing theexposed portion of the conducting element, and in that the connectionmeans are fastened by adhesive bonding to the free part of the substrateand are connected via electrical bonding means to that exposed portionof the conducting element facing the free part.

According to a second embodiment, the structure, with the conductingelement deposited on the backing sheet, is characterized in that theconducting element is sandwiched between the tie sheet and the backingsheet, and at least the backing sheet and, when it is present, theadditional sheet are, at least on one of their sides, placed set backrelative to the associated free edge of the transparent substrate so asto leave space for an exposed portion of the conducting element, and inthat the connection means are fastened by adhesive bonding and/or bymechanical crimping to the exposed portion of the conducting element.

According to a third embodiment, the structure, with the conductingelement deposited on the backing sheet and including the covering sheet,is characterized in that the conducting element deposited on the backingsheet is placed opposite the tie sheet and sandwiched between thebacking sheet and the covering sheet, the covering sheet being, at leaston one of its sides, set back toward the interior of the structurerelative to the associated free edge of the transparent substrate inorder to leave space for an exposed portion of the conducting element,and in that the connection means are fastened by adhesive bonding and/orby mechanical crimping to the exposed portion of the conducting element.

According to a fourth embodiment, the structure the conducting elementis deposited on the substrate, is characterized in that at least the tiesheet and, when it is present, the covering sheet are, on at least oneof their sides, set back toward the interior of the structure relativeto the associated free edge of the transparent substrate in order toleave the exposed portion of the conducting element accessible, and inthat the connection means are fastened by adhesive bonding and/or bymechanical crimping to the exposed portion of the conducting element.

According to one feature, the conducting element is a silver-based metallayer. As a variant, the conducting element consists of a mesh ofconducting wires, preferably copper wires.

According to another feature, the connection means consist of a flatconductor such as a busbar or a conductive foam tape.

Advantageously, all of the periphery of the first substrate of the facesituated toward the interior of the structure or else the free part ofsaid first substrate is covered with an enamel.

Preferably, the exposed portion corresponds, in the manner of a frame,to the entire periphery of one of the faces of the conducting element.

According to another feature, the backing sheet is made of a plastic,for example PET or one based on one of the following materials:polycarbonate, polymethyl (meth)acrylate, polyethersulfone,polyetherketone and styrene-acrylonitrile copolymers. Moreover, the tiesheet, the additional sheet and the covering sheet are made of aplastic, such as polyvinyl butyral, polyurethane or ethylene-vinylacetate.

In its use, the structure is, for example, fitted into a frame, theinner part of which is metallic, the connection means pressing againstsaid inner part.

Finally, the structure may be joined to the front face of a display,such as a plasma display, and connected to the electrical ground of thisdisplay.

Other advantages and features of the invention will now be described ingreater detail in conjunction with the appended drawings in which:

FIG. 1 is a sectional view of an electromagnetic shielding structure fora display according to the prior art; and

FIGS. 2, 3 a, 3 b, 4 a, 4 b and 5 are sectional views of anelectromagnetic shielding structure according to four embodiments of theinvention respectively.

Illustrated in FIGS. 2, 3 a, 3 b, 4 a, 4 b and 5 by way of non limitingexamples are four embodiments of an electromagnetic shielding structure2 intended for example to be joined to the front face of a display (notillustrated here), such as a plasma display. Shown partially is just theframe 5 of the display into which the shielding structure 2 is fitted.The invention provides the electrical connection of the shieldingstructure to the electrical ground of the display.

For more details about the embodiments of the shielding structure andtheir variants, the reader may refer to French patent application FR03/04636.

The shielding structure 2 comprises at least a first transparentsubstrate 20, preferably of the glass type, optionally a secondtransparent substrate 21 of the glass type, and a conductingelectromagnetic shielding element 30 associated with the firstsubstrate. Electrical connection means 40 are attached and intended toelectrically connect the conducting element 30 to a conducting part 50of the display, such as the metal interior of the frame 5 that supportsthe shielding structure for joining it to the display, the metal innerpart 50 being intended to be connected to the ground of the display.

The shielding structure 2 is thus placed in the frame 5 intended to bejoined to the display by standard mechanical fastening means. The firstglass substrate 20 is intended to face the viewer, this first substratebeing defined in the rest of the description as the front side of thestructure, whereas the second substrate 21 is intended to face thedisplay, i.e. on the rear side of the structure.

Advantageously, the first substrate 20 is made of toughened glass, inorder to withstand impacts, and has, on its external face on the sidefacing the viewer, an antireflection coating.

The conducting element 30 consists, for example, of a mesh of metalwires, advantageously copper wires, said mesh being deposited on atransparent plastic backing sheet 31, for example made of PET or onebased on one of the following materials: polycarbonate, polymethyl(meth)acrylate, polyethersulfone, polyetherketone andstyrene-acrylonitrile copolymers.

As a variant, the conducting element 30 may instead be a metal coating,such as one based on silver, deposited on the plastic backing sheet 31or else deposited directly on the internal face of the substrate 20facing the interior of the structure.

The structure 2 also includes a transparent tie sheet 22 made of aplastic, such as polyvinyl butyral or polyurethane or ethylene-vinylacetate, placed against the first substrate 20.

The tie sheet 22, when the conducting element 30 is attached to thebacking sheet 31, ties the conducting element to the first substrate 20by the backing sheet 31 of the conducting element being joined to saidtie sheet 22 after heating the plastics.

When the conducting element 30 is deposited directly on the substrate20, the tie sheet 22 in particular ties the substrate to any otherelement.

Unlike the prior art, for which the electrical connection of theconducting shielding element is made by flat conductors that depend andcover the edges of the conducting element and of the backing sheet (FIG.1), the connection according to the invention is obtained as will beexplained, directly on one of the faces of the conducting element andattaching thereto the connection means after the structure has beenmanufactured.

In the embodiment illustrated in FIG. 2, the tie sheet 22 does notextend back to the edges of the first glass substrate 20 but is set backtoward the interior of the structure so as to leave space for a freepart 20 a advantageously over the entire internal periphery of the glasssubstrate, this free part of the substrate preferably being covered withblack enamel.

The connection means 40 are fixed to this free part 20 a and extend overthe inner conducting part 50 of the frame 5. The connection means 40consist, for example, of a busbar, for example fixed by adhesivebonding, on this free part 20 a of the periphery of the glass substrate,the black enamel concealing these connection means when viewed from theoutside.

As regards the conducting element 30 positioned on the backing sheet 31and facing the tie sheet 22, this extends beyond the tie sheet 22 sothat a portion 32 of its face 30 a that faces the tie sheet 22 ispositioned opposite the free part 20 a to which the connection means 40are fixed. The portion 32 preferably corresponds to the entire peripheryof one of the faces, here the face 30 a, of the conducting element. Theelectrical bonding between the connection means 40 and the portion 32 ofthe conducting element facing the connection means is provided by anysuitable electrical bonding means 41, for example a layer of conductiveadhesive or a conductive adhesive tape of the copper type.

In this embodiment, the structure includes the second glass substrate21, which has dimensions equivalent to the backing sheet 31. It isjoined to the backing sheet via an additional sheet 23 of plastic, suchas PVB, with dimensions equivalent to those of the backing sheet 31 andof the glass substrate 21.

As a variant (but not illustrated), it is possible for the structure notto have a second glass substrate, and the backing sheet 31 then directlyforms the rear face that is intended to be joined to the display.

In the second embodiment, illustrated in FIGS. 3 a and 3 b, for whichthe conducting element 30 remains sandwiched between the backing sheet31 and the tie sheet 22, it is unnecessary for the tie sheet 22 to bereduced in area relative to the first glass substrate. On the otherhand, the backing sheet 31 is set back relative to the conductingelement so as to leave exposed a portion 32 of its face 30 b, this facebeing joined to the backing sheet 31. This portion 32, which preferablycorresponds to the entire periphery of the face 30 b, is then directlyaccessible from the rear of the structure in order for the connectionmeans 40 to be applied and mechanically pressed thereon.

The connection means 40 may for example consist of a busbar. This busbaris, for example, pressed against the portion 32 of the face 30 b of theconducting element by the clamping of a metal tab 51 integral with theelectrical grounding frame 5 (FIG. 3 a), or else to be pressed againstthe portion 32 by a part 52 of the frame of the display, which will beinserted between the structure and the conducting part 50 of the frame(FIG. 3 b). The mechanical clamping of the connection means 40 is infact performed by any suitable means within the competence of a personskilled in the art.

As a variant, the connection means 40 may consist of a conductive foamthat is adhesive, in order to fasten the portion 32 of the conductingelement to the conducting part 50 of the frame, this foam beingdeposited by an extrusion or injection-molding technique.

In this second embodiment, the second glass substrate 21, which isfastened to the backing sheet 31 via an additional sheet 23 of plastic,such as PVB, has the dimensions of the additional sheet and of thebacking sheet.

As a variant (but not illustrated) and as in the first embodiment, it ispossible for the structure not to include a second glass substrate 21,and the backing sheet 31 therefore directly constitutes the rear facethat is intended to be joined to the display.

In the third embodiment (FIGS. 4 a and 4 b), the conducting element 30is placed, not so as to be sandwiched between the tie sheet 22 and thebacking sheet 21, but on the opposite side of the tie sheet 22. In thiscase, the structure 1 furthermore includes a transparent covering sheet24 made of plastic, such as PVB. This covering sheet 24 is placedagainst the conducting element 30 so as to form a protective layer. Inaddition, it ties the conducting element 30 to the second substrate 21by said covering sheet being joined to said substrate.

This arrangement of the conducting element 30 placed on the rear side ofthe structure, and therefore on the opposite side from the viewer, meansthat the PET backing sheet 31 is placed on the same side as the viewer.When the conducting element is a copper mesh, the bonding interfacebetween the mesh and the PET has, as is known, a black pigment that isthen on the same side as the viewer. This configuration therefore hasthe advantage of attenuating the red reflection from the copper of theconducting element, the visual comfort of the viewer being furtherimproved.

In this third embodiment, the tie sheet 22 and the backing sheet 31 donot need to be set back relative to the first substrate 20, and may havethe same dimensions as the first substrate. The conducting element 30also extends over the entire area of the backing sheet 31, and thereforeright to the edges of the substrate 20. However, the covering sheet 24is smaller in size, being set back toward the interior of the structure,so as to leave accessible a portion 32, preferably over the entireperiphery, of the face 30 a on the opposite side from the backing sheet31. The second substrate 21, which is fastened to the covering sheet 24,has the dimensions of said sheet.

In a manner similar to the second embodiment, the connection means 40are placed directly, via the rear, against the portion 32 of the face 30b of the conducting element. The alternative versions of the connectionmeans 40 and of their application are also those described in the secondembodiment.

In the fourth embodiment (FIG. 5), the conducting element 30 isdeposited on the internal face of the first substrate 20, toward theinterior of the structure, the conducting element being in the form of ametal coating, such as one based on silver. The structure includes a tiesheet 22 which allows the first substrate 20 to be joined to the secondglass substrate if it is present (not illustrated here) or joineddirectly to the display. The structure may optionally include a coveringsheet 24 made of plastic such as PVB, which makes it possible to providea function other than the function fulfilled by the tie sheet 22, or toprotect the tie sheet 22 if the latter is made of a material that can beeasily scratched for example, and therefore to constitute a sheet forjoining the structure to the second glass substrate if it is present(not illustrated here in FIG. 5), or else a sheet for joining thestructure directly to the screen.

In this fourth embodiment, the sheets 22 and 24 are set back toward theinterior of the structure so as to leave an exposed portion 32accessible, preferably over the entire periphery, of the face 30 b ofthe conducting element.

In a manner similar to the second and third embodiments, the connectionmeans 40 are placed directly via the rear against the portion 32 of theface 30 b of the conducting element. The alternative versions of theconnection means 40 and of their application are also those described inthe second embodiment, these being illustrated here by the mechanicalclamping tabs 51.

As in the first embodiment, it should be noted that the substrate 20 ofthe three other embodiments is covered, over its entire periphery and onits internal face toward the interior of the structure, with a blackenamel that allows all the electrical connections to be concealed.

Thus, according to the invention, at least one of the backing sheet 31of the conducting element, the tie sheet 22 and the additional sheet 23or the covering sheet 24, when one is present, is, at least on one ofits sides, placed set back toward the interior of the structure relativeto the associated free edge of the first substrate 20 so as to leave aportion 32 of the conducting element bare or exposed on at least one ofthe faces 30 a or 30 b thereof. The connection means 40 that connect theconducting element 30 to the electrical ground of the display areadvantageously a flat conductor such as a busbar or a conductive foamtape that is connected to the exposed portion 32 of one of the faces 30a or 30 b of the conducting element 30 by adhesive bonding or bymechanical clamping.

The connection means 40 are thus made independent of the conductingelement 30, the shielding structure not needing to intrinsically includethe electrical connection means, thereby making it easier to manufacturethe shielding structure and the displays.

1. An electromagnetic shielding structure, comprising: a conductingelement; a transparent tie sheet mounted on said conducting element; afirst transparent substrate mounted on said tie sheet; a backing sheetcontacting a back portion of said conducting element; a plastic sheetwhich contacts said backing sheet; a second transparent substrate whichcontacts said plastic sheet; and an electrical connection memberconnected with said conductive element wherein at least one of saidtransparent tie sheet, said backing sheet, said plastic sheet and saidsecond transparent substrate is set back with respect to at least onefree edge portion of said substrate so as to form an exposed portionwithin which said electrical connection member is positioned and whereinsaid connection member comprises a substantially flat conductor which isconnected to said exposed portion of said conducting element.
 2. Theelectromagnetic shielding structure as claimed in claim 1, wherein onlysaid transparent tie sheet is set back to form said exposed portion. 3.The electromagnetic shielding structure as claimed in claim 1, whereineach of said backing sheet, said sheet of plastic and said secondtransparent substrate are set back to form said exposed portion.
 4. Theelectromagnetic shielding structure as claimed in claim 1, whichcomprises a frame within which said electrical connection member ispositioned.
 5. The electromagnetic shielding structure as claimed inclaim 1, wherein an enamel covering is provided on one of substantiallyall of a peripheral portion of the first substrate and a free part ofsaid first substrate.
 6. The electromagnetic shielding structure asclaimed in claim 1, wherein the conducting element comprises asilver-based metal layer.
 7. The recapty structures claimed in claim 1,where in the conducting element comprises a mesh of conducting wires. 8.The structures claim in claimed 1, wherein the flat conductor comprisesa bus bar or a conductive foam tape.
 9. The structures claimed in claim1, wherein the backing sheet is made of a plastic, PET, or materialbased on one of the following materials: Polycarbonate, polymethyl(meth) acrylate, polyethersulfone, polyether-kethone andstyrene-acrylonitrile compolymers.
 10. The structures claimed in claim1, wherein the tie sheet, the additional sheet, and the covering sheetare made of one of a plastic, polyvinyl butyral, polyurethane, orethylene-vinyl acetate.
 11. The structures claimed in claim 1, thestructure being joined to a front face of a display, and connected to anelectrical ground of the display.